Distribution, characterization, and geochemical controls of elements of concern in uranium mine tailings, Key Lake, Saskatchewan, Canada

The distribution of As, Mo, Ni and Se in the aqueous and solid phases of U mine tailings in the Deilmann Tailings Management Facility (DTMF), located at the Key Lake mine in northern Saskatchewan, Canada, was defined using as-discharged tailings samples collected monthly starting in 1996 and core samples collected from the DTMF from 3 locations on 3 occasions between 2004 and 2009. These data indicated that the DTMF can be divided into two geochemical zones; tailings generated from the Deilmann ore body between 1996 and 2000 and tailings from the McArthur River ore body, mined after July 2000. The Deilmann tailings solids are generally characterized by greater elemental concentrations than those in the McArthur River tailings, particularly for As, Co and Ni. These elevated concentrations are attributed to the abundance of Ni–Co–As–S minerals in this ore. The mean aqueous concentrations of As, Mo, Ni, and Se are 3.7, 23.2, 0.14, and 0.02 mg L⁻¹, respectively, in the Deilmann porewaters and 0.20, 4.16, 0.06, and 0.03 mg L⁻¹, respectively, in the McArthur River porewaters. Similarly, the mean As, Mo, Ni, and Se solid phase concentrations are 5.89 × 10³, 69.9, 3.20 × 10³, and 17.4 μg g⁻¹, respectively, for the Deilmann tailings and 440, 13.6, 551, and 3.03 μg g⁻¹ in the McArthur River tailings. Statistically, pH remained unchanged from the time of discharge while Eh values have remained oxic with no significant change between the two tailings types over 15 a of residence time. Results from sequential extractions, thermodynamic modeling, and results of complimentary research indicated that ferrihydrite solubility is the dominant control on aqueous As concentrations and also plays a role in controlling dissolved Mo, Ni and Se.     

Sphene and zircon in the Highland Range volcanic sequence (Miocene, southern Nevada, USA): elemental partitioning, phase relations, and influence on evolution of silicic magma

Sphene is prominent in Miocene plutonic rocks ranging from diorite to granite in southern Nevada, USA, but it is restricted to rhyolites in coeval volcanic sequences. In the Highland Range volcanic sequence, sphene appears as a phenocryst only in the most evolved rocks (72?C77 mass% SiO₂; matrix glass 77?C78 mass% SiO₂). Zr-in-sphene temperatures of crystallization are mostly restricted to 715 and 755°C, in contrast to zircon (710?C920°C, Ti-in-zircon thermometry). Sphene rim/glass Kds for rare earth elements are extremely high (La 120, Sm 1200, Gd 1300, Lu 240). Rare earth elements, especially the middle REE (MREE), decrease from centers to rims of sphene phenocrysts along with Zr, demonstrating the effect of progressive sphene fractionation. Whole rocks and glasses have MREE-depleted, U-shaped REE patterns as a consequence of sphene fractionation. Within the co-genetic, sphene-rich Searchlight pluton, only evolved leucogranites show comparable MREE depletion. These results indicate that sphene saturation in intruded and extruded magmas occurred only in highly evolved melts: abundant sphene in less silicic plutonic rocks represents a late-stage ??bloom?? in fractionated interstitial melt.     

Glaciation and ~ 770 Ma Ediacara (?) Fossils from the Lesser Karatau Microcontinent,Kazakhstan

The Cambrian explosion, c. 530–515 Ma heralded the arrival of a diverse assembly of multicellular life including the first hard-shelled organisms. Fossils found in Cambrian strata represent the ancestors of most modern animal phyla. In contrast to the apparent explosiveness seen in the Cambrian fossil record, studies of molecular biology hint that the diversification observed in Cambrian strata was rooted in ancestry extending back into the Ediacaran (635–542 Ma). Fossil evidence for this mostly cryptic phase of evolution is derived from the soft-bodied fossils of the Ediacaran biota found throughout the world and bilaterian embryos found in the Doushantuo lagerstätte in South China. The first appearance of Ediacara fauna is thought to have followed the last of the ~ 750–635 Ma Neoproterozoic glacial episodes by 20–30 million years. In this paper, we present evidence for the oldest discovery of the ‘Ediacara’ discoidal fossils Nimbia occlusa and Aspidella terranovica (?) that predate the early Cryogenian glaciations by more than fifty million years. There is considerable disagreement over the significance of discoidal Ediacaran fossils, but our findings may support earlier suggestions that metazoan life has roots extending deeper into the Proterozoic Eon. We also confirm the presence of a Late Cryogenian (e.g. “Marinoan”) glaciation on the Lesser Karatau microcontinent including dropstones and striated clasts within the glacial strata.     

Excess air during aquifer storage and recovery in an arid basin (Las Vegas Valley, USA)

The Las Vegas Valley Water District in Nevada, USA, has operated an artificial recharge (AR) program since 1989. In summer 2001, observations of gas exsolving from tap water prompted a study that revealed total dissolved gas (TDG) pressures approaching 2?atm with a gas composition that it is predominantly air. Measurements of TDG pressure at well heads and in the distribution system indicated two potential mechanisms for elevated TDG pressures: (1) air entrainment during AR operations, and (2) temperature changes between the winter recharge season and the summer withdrawal season. Air entrainment during pumping was investigated by intentionally allowing the forebay (upstream reservoir) of a large pumping station to drawdown to the point of vortex formation. This resulted in up to a 0.7?atm increase in TDG pressure. In general, the solubility of gases in water decreases as the temperature increases. In the Las Vegas Valley, water that acquired a modest amount of dissolved gas during winter artificial recharge operations experienced an increase in dissolved gas pressure (0.04?atm/°C) as the water warmed in the subsurface. A combination of air entrainment during AR operations and its amplification by temperature increase after recharge can account for most of the observed amounts of excess gas at this site.     

On the utility of identification schemes for digital earth science data: an assessment and recommendations

In recent years, a number of data identification technologies have been developed which purport to permanently identify digital objects. In this paper, nine technologies and systems for assigning persistent identifiers are assessed for their applicability to Earth science data (ARKs, DOIs, XRIs, Handles, LSIDs, OIDs, PURLs, URIs/URNs/URLs, and UUIDs). The evaluation used four use cases that focused on the suitability of each scheme to provide Unique Identifiers for Earth science data objects, to provide Unique Locators for the objects, to serve as Citable Locators, and to uniquely identify the scientific contents of data objects if the data were reformatted. Of all the identifier schemes assessed, the one that most closely meets all of the requirements for an Unique Identifier is the UUID scheme. Any of the URL/URI/IRI-based identifier schemes assessed could be used for Unique Locators. Since there are currently no strong market leaders to help make the choice among them, the decision must be based on secondary criteria. While most publications now allow the use of URLs in citations, so that all of the URL/URI/IRI based identification schemes discussed in this paper could potentially be used as a Citable Locator, DOIs are the identification scheme currently adopted by most commercial publishers. None of the identifier schemes assessed here even minimally address identification of scientifically identical numerical data sets under reformatting.     

The progress on remote sensing technology in identifying tropical forest degradation: a synthesis of the present knowledge and future perspectives

Since the launch of the first satellite in 1972, ecologists have been equipped with new tools to address the degradation of tropical forests, previously limited by field-based methods. This article is a review of the state of remote sensing technology in characterizing the degradation of tropical forest. The factors responsible for the structural and functional degradation of the tropical forest and its likely impacts are described in view of generating remote sensing based inputs. In order to assess the degradation and utility of geo-informatics tools, 32 parameters are identified. The research developments at different levels of information extraction from the historic to recent periods are elaborated, and future challenges are predicted. The article concludes that an additional momentum of research is required to answer many unresolved questions of tropical forest degradation.     

Tumbi Landslide, Papua New Guinea: rainfall induced?

On 24 January 2012, a fatal landslide with an estimated volume of 3 Mm³ hit villagers and infrastructure in the Tagali Valley, Southern Highlands Province, Papua New Guinea (PNG). Although a moderate event by PNG standards, the associated human casualties and infrastructure destruction give a human as well as a scientific need to review the potential causes for the event. PNG experiences numerous landslides annually, most of which are trigged either by rainfall events or seismic activity. Here, we review the short-term rainfall patterns leading up to the slope failure at Tumbi Quarry and compare the rainfall accumulations obtained over durations of 30, 60 and 90 days prior to the landslide, with comparable rainfall accumulations obtained for other failures observed in PNG over a 12-year period. Additionally, a review of long-term rainfall over a period of 6 months prior to the failure is completed as well as an assessment of seismic activity. Based on our analysis, we believe a seismic trigger to be very unlikely, while the increase in rainfall in the 2 weeks prior to the failure in conjunction with a high-intensity rainfall event at the end of October 2011 could have had a greater influence in enhancing rather than restraining slope failure. This, in addition to natural denudational processes, geological structure and the anthropogenic activity in the vicinity of the landslide, could all have served to affect slope stability.     

Eruptive history of the Barombi Mbo Maar, Cameroon Volcanic Line, Central Africa: Constraints from volcanic facies analysis

his study presents the first and detail field investigations of exposed deposits at proximal sections of the Barombi Mbo Maar (BMM), NE Mt Cameroon, with the aim of documenting its past activity, providing insight on the stratigraphic distribution, depositional process, and evolution of the eruptive sequences during its formation. Field evidence reveals that the BMM deposit is about 126m thick, of which about 20m is buried lowermost under the lake level and covered by vegetation. Based on variation in pyroclastic facies within the deposit, it can be divided into three main stratigraphic units: U₁, U₂ and U₃. Interpretation of these features indicates that U₁ consists of alternating lapilli-ash-lapilli beds series, in which fallout derived individual lapilli-rich beds are demarcated by surges deposits made up of thin, fine-grained and consolidated ash-beds that are well-defined, well-sorted and laterally continuous in outcrop scale. U₂, a pyroclastic fall-derived unit, shows crudely lenticular stratified scoriaceous layers, in which many fluidal and spindle bombs-rich lapilli-beds are separated by very thin, coarse-vesiculatedash-beds, overlain by a mantle xenolith- and accidental lithic-rich explosive breccia, and massive lapilli tuff and lapillistone. U3 displays a series of surges and pyroclastic fall layers. Emplacement processes were largely controlled by fallout deposition and turbulent diluted pyroclastic density currents under “dry” and “wet” conditions. The eruptive activity evolved in a series of initial phreatic eruptions, which gradually became phreatomagmatic, followed by a phreato-Strombolian and a violent phreatomagmatic fragmentation. A relatively long-time break, demonstrated by a paleosol between U₂ and U₃, would have permitted the feeding of the root zone or the prominent crater by the water that sustained the next eruptive episode, dominated by subsequent phreatomagmatic eruptions. These preliminary results require complementary studies, such as geochemistry, for a better understanding of the changes in the eruptive styles, and to develop more constraints on the maar’s polygenetic origin.     

Observational Evidence for a Double-Helix Structure in CMEs and Magnetic Clouds

We compare recent observations of a solar eruptive prominence as seen in extreme-UV light on 30 March 2010 by the Solar Dynamics Observatory (SDO) with the multi-tube model for interplanetary magnetic clouds (Osherovich, Fainberg, Stone, Geophys. Res. Lett. 26, 2597, 1999). Our model is based on an exact analytical solution of the plasma equilibrium with magnetic force balanced by a gradient of scalar gas pressure. Topologically, this solution describes two magnetic helices with opposite magnetic polarity embedded in a cylindrical magnetic flux tube that creates magnetic flux inequality between the two helices by enhancing one helix and suppressing the other. The magnetic field in this model is continuous everywhere and has a finite magnetic energy per unit length of the tube. These configurations have been introduced as MHD bounded states (Osherovich, Soln. Dannye 5, 70, 1975). Apparently, the SDO observations depict two non-equal magnetically interacting helices described by this analytical model. We consider magnetic and thermodynamic signatures of multiple magnetic flux ropes inside the same magnetic cloud, using in situ observations. The ratio of magnetic energy density to bulk speed solar wind energy density has been defined as a solar wind quasi-invariant (QI). We analyze the structure of the QI profile to probe the topology of the internal structure of magnetic clouds. From the superposition of 12 magnetically isolated clouds observed by Ulysses, we have found that the corresponding QI is consistent with our double helix model.